The cetane number of a fuel (e.g. Diesel) provides a measure of the ignition characteristics when used in compression ignition engines. The cetane number scale ranges from 0 to 100, but is typically tested in the range 30 to 65.
It is useful to know the cetane number of a fuel in order to provide the most efficient combustion in modern diesel engines that have low compression ratios. Modern diesel engines are quite sensitive to fuel with cetane numbers below 50.
In order to determine cetane number, traditionally a standard testing technique uses a standard single cylinder of a four stroke cycle Diesel engine having a variable compression ratio. The principle behind this technique is to determine the compression ratio that corresponds to a pre-defined auto ignition delay. The auto ignition delay is determined by measuring, during the combustion cycle, two different times. The first when the injector injects the fuel and the second when the combustion starts. The difference of these two times gives the auto ignition delay.
In this manner, cetane number and compression ratio are related using a calibration curve, and the cetane number can be determined. The calibration utilises the points from alpha-methylnapthalene and n-cetane that are arbitrarily assigned to cetane numbers 0 and 100.
The above procedure requires a special engine and cannot be performed on a standard diesel engine. It is an object of the invention to determine cetane number using a standard engine and furthermore without the use of additional sensors.